Specifies the substitution method for determining the insertion loss of ducted silencers. Sets out the requirements for determining: the sound power level, in frequency bands, of the flow noise generated by silencers; the insertion loss, in frequency bands, of silencers with and without air flow; the total pressure loss of silencers with air flow. Applies to silencers for ventilating and air-conditioning systems which are usually connected to ducts or splitter absorbers mounted in ducts.